Roll Dart SDK from 54cc31c to 1b845f6 (1 revision) (#34705)

Author: skia-flutter-autoroll

DEPS

@@ -35,7 +35,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '54cc31cd98db9314b8aae563ece56a9b4b3e13a3',
+  'dart_revision': '1b845f6a8c90321d6317095c322b100ddd5dcf36',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py